This invention relates in general to fluid actuators for causing movement of a piston relative to a cylinder. In particular, this invention relates to an air/oil intensifier type of fluid actuator having multiple sensors for measuring various operational characteristics of the intensifier cylinder.
Fluid actuators are well known devices which are adapted to generate mechanical movement in response to the application of pressurized fluid, such as air or oil. A basic fluid actuator includes a hollow cylinder having a piston sidably disposed therein. The outer circumferential surface of the piston slidably and sealingly engages the inner circumferential surface of the cylinder so as to divide the interior of the cylinder into first and second chambers. When a pressurized fluid is supplied to the first chamber and the second chamber is vented, a pressure differential is created across the piston. This pressure differential causes the piston to slide relative to the cylinder in a first direction. Similarly, when a pressurized fluid is supplied to the second chamber and the first chamber is vented, the pressure differential created across the piston causes it to slide relative to the cylinder in a second direction. One or more fluid valves are usually provided to control the supply of pressurized fluid to and the venting of the two chambers of the cylinder so as to effect movement of the piston in a desired manner.
Typically, a rod is connected to the piston for movement therewith. The rod extends outwardly from the cylinder into engagement with a workpiece. Thus, when the piston is moved within the cylinder as described above, the workpiece is moved therewith. The magnitude of the force which is generated against the workpiece is equal to the product of the pressure of the fluid in the chamber and the surface area of the piston exposed to that pressurized fluid. Thus, for example, if the magnitude of the pressurized fluid is one hundred pounds per square inch (p.s.i.) and the surface area of the piston is two square inches, then the magnitude of the force exerted by the piston against the workpiece will be two hundred pounds. Fluid actuators of this general type are commonly used in a variety of applications.
In some applications, however, the magnitude of the pressurized fluid available for use by the fluid actuator is limited. For example, in a typical manufacturing facility, pressurized air may be generated by a central supply system at a standard pressure, such as one hundred p.s.i., for the entire facility. At the same time, the magnitude of the force necessary for the fluid actuator to perform a given task may be relatively large, such as one thousand pounds. If a basic fluid actuator structure as described above were to be used to perform this task, the piston would have to very large (ten square inches in this example) in order to generate the necessary force. Obviously, it is undesirable from several standpoints to provide such a physically large piston.
To address the problem of generating relatively large forces using limited fluid pressures and relatively small pistons, it is known to modify the basic fluid actuator structure to generate an increased amount of force. These modified fluid actuator structures, which are commonly referred to as intensifiers, use multiple interacting pistons to multiply the forces produced by the pressurized fluid against the pistons, while maintaining relatively small sizes for the pistons. A typical intensifier structure includes a cylinder which is divided by an internal manifold into two working areas. In the first working area, a first piston is provided which divides the interior thereof into first and second chambers. A rod extends from the first piston through the manifold into the second working area. In the second working area, a second piston is provided which divides the interior thereof into first and second chambers.
When pressurized fluid is supplied to the first chamber of the first working area, a first force is generated against the first piston as described above. Movement of the first piston causes corresponding movement of the first rod in the first chamber of the second working area. The first chamber of the second working area is typically filled with a relatively incompressible liquid, such as oil. Thus, a second force is generated against the second piston because of the movement of the rod. The rod has a much smaller surface area than the first piston. Thus, the magnitude of the pressure generated in the first chamber of the second area against the second piston is multiplied relative to the original pressure exerted against the first piston. This multiplied pressure is applied against the surface area of the second piston and generates a multiplied force. A second rod connected to the second piston transmits the multiplied force to a workpiece.
Air/oil intensifiers are commonly used in manufacturing processes for performing systematic functions in a repeatable manner. For example, an intensifier can be adapted to operate a punch tool to perform a cut-out operation on a succession of workpieces traveling along a conveyor system. Ideally, the air/oil intensifier would perform the exact operation and obtain exactly the same result for every workpiece. However, for various reasons, such as misalignment of the workpiece, differences between the sizing of the workpieces, or malfunction of the air/oil intensifier, variations may occur in the manufacturing process. To insure that the workpieces are being manufactured within design tolerances, it is desirable to monitor the operation of the air/oil intensifier. One well known method for monitoring the operation of a manufacturing process involves the use of statistical process control. Statistical process control is the systematic measuring of tolerances or other criteria for one or more stages in the manufacturing process. These measurements are then plotted statistically so that trends in the manufacturing can be ascertained. By using statistical process control methods, variations in the manufacturing process which can result in the manufacture of defective workpieces can be determined in advance and corrected before such defective workpieces are actually manufactured.
In the past, the application of statistical process control methods to the manufacture of workpieces with an air/oil intensifier has involved the systematic inspection of the workpiece after the manufacturing operation has been performed by the air/oil intensifier. However, it is relatively time consuming and expensive to physically inspect the workpieces in this manner. Additionally, while a physical inspection of the workpiece may reveal the presence of a defect or a trend toward manufacturing a defect, the cause of such defect may not be readily ascertainable. This is particularly true when the cause of the manufacturing defect lies in the operation of the air/oil intensifier. Thus, it would be desirable to provide an improved structure for an air/oil intensifier which facilitates the application of statistical process control methods to the operation thereof.